NETWORK WORKING GROUP N. Williams Internet-Draft Sun Intended status: Standards Track M. Richardson |Expires: January 27, 2008 SSW | July 26, 2007 Better-Than-Nothing-Security: An Unauthenticated Mode of IPsec | draft-ietf-btns-core-04.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. | This Internet-Draft will expire on January 27, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). |Williams & Richardson Expires January 27, 2008 [Page 1] |Internet-Draft BTNS IPsec July 2007 Abstract This document specifies how to use the Internet Key Exchange (IKE) protocols, such as IKEv1 and IKEv2, to setup "unauthenticated" security associations (SAs) for use with the IPsec Encapsulating Security Payload (ESP) and the IPsec Authentication Header (AH). No | changes to IKEv2 bits-on-the-wire are required, but Peer | Authorization Database (PAD) and Security Policy Database (SPD) | extensions are specified. Unauthenticated IPsec is herein referred | to by its popular acronym, "BTNS" (Better Than Nothing Security). Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . . 3 2. BTNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . 6 | 3.1. Example #1: A security gateway . . . . . . . . . . . . . . . 6 | 3.2. Example #2: A mixed end-system . . . . . . . . . . . . . . . 8 | 3.3. Example #3: A BTNS-only system . . . . . . . . . . . . . . . 9 | 3.4. Miscellaneous comments . . . . . . . . . . . . . . . . . . . 10 | 4. Security Considerations . . . . . . . . . . . . . . . . . . 11 | 4.1. Connection-Latching and Channel Binding . . . . . . . . . . 11 | 4.2. Leap-of-Faith (LoF) for BTNS . . . . . . . . . . . . . . . . 11 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12 | 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 | 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 | 7.1. Normative References . . . . . . . . . . . . . . . . . . . . 14 | 7.2. Informative References . . . . . . . . . . . . . . . . . . . 14 | Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 15 | Intellectual Property and Copyright Statements . . . . . . . 16 |Williams & Richardson Expires January 27, 2008 [Page 2] |Internet-Draft BTNS IPsec July 2007 1. Introduction Here we describe how to establish unauthenticated IPsec SAs using | IKEv2 [RFC4306] and unauthenticated public keys. No new on-the-wire | protocol elements are added to IKEv2. The [RFC4301] processing model is assumed. This document does not define an opportunistic BTNS mode of IPsec | whereby nodes may fallback to unprotected IP when their peers do not | support IKEv2, nor does it describe "leap-of-faith" modes, or "connection latching." See [I-D.ietf-btns-prob-and-applic] for the applicability and uses of | BTNS and definitions of these terms. | This document describes BTNS in terms of IKEv2 and [RFC4301]'s | concepts. There is no reason why the same methods cannot be used | with IKEv1 [RFC2408] [RFC2409] and [RFC2401], however, those | specifications do not include the PAD concepts, and therefore it may | not be possible to implement BTNS on all compliant RFC2401 | implementations. 1.1. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. |Williams & Richardson Expires January 27, 2008 [Page 3] |Internet-Draft BTNS IPsec July 2007 2. BTNS | The IPsec processing model is hereby modified as follows: o A new ID type is added, 'PUBLICKEY'; IDs of this type have public keys as values. This ID type is not used on the wire. | o A BTNS-specific PAD entry. This entry MUST be the last entry in | the PAD when BTNS is enabled. A peer that matches no other PAD | entries is to be "authenticated" by verifying that the signature | in its AUTH payload in the IKEv2 exchange with the public key from | the peer's CERT payload. The peer's ID MUST then be coerced to be | of 'PUBLICKEY' type with the peer's public key as its value. | o To accomplish the above, search the PAD as normal, with the ID | provided by the peer. If it matches do normal processing. If the | ID asserted by a peer does not match any PAD entry, then a BTNS- | enabled IPsec implementation replaces the ID with into the new ID | of type "PUBLICKEY" that is created by extracting the public key | from the IKE CERT payload. | o The PAD is searched again, using this new ID type and value. If | there is a match, the associated PAD entry (which will be a BTNS | entry) is used to control the SPD search. | o If there is no match, the IKE SA is rejected o A new flag for SPD entries: 'BTNS_OK'. Traffic to/from peers that | match the BTNS PAD entry will match only SPD entries that have the BTNS_OK flag set. The SPD may be searched by address or by ID (of | type PUBLICKEY, for BTNS peers), as per the IPsec processing model | [RFC4301]; searching by ID in this case requires creation of SPD | entries that are bound to public key values (this could be used to | build "leap-of-faith" [I-D.ietf-btns-prob-and-applic] Section 4.2 | behaviour, for example). Nodes MUST reject IKE_SA proposals from peers that match non-BTNS PAD entries but fail to authenticate properly. | Nodes wishing to be treated as BTNS nodes by their peers MUST include | bare RSA key CERT payloads. Nodes MAY also include any number of | certificates that bind the same public key. These certificates need | not to have been pre-shared with their peers (e.g., because ephermal, | self-signed). RSA keys for use in BTNS may be generated at any time, | but "connection latching" [I-D.ietf-btns-connection-latching] | requires that they remain constant between IKEv2 exchanges that are | used to establish SAs for latched connections. |Williams & Richardson Expires January 27, 2008 [Page 4] |Internet-Draft BTNS IPsec July 2007 | To preserve standard IPsec access control semantics the BTNS PAD | entry MUST be last (lowest priority), and it MUST have ID constraints | that do not overlap those of other PAD entries. | This can easily be implemented by searching the PAD twice. Once when | BTNS peers authenticate and a second time when BTNS peers negotiate | child SAs. In the first pass the PAD is searched for a matching PAD | entry as usual, and in the second it is searched to make sure that | BTNS peers' asserted child SA traffic selectors do not conflict with | non-BTNS PAD entries. |Williams & Richardson Expires January 27, 2008 [Page 5] |Internet-Draft BTNS IPsec July 2007 3. Usage Scenarios In order to explain the above rules a number of scenarios will be | examined. The goal here is to persuade the reader that the above | rules are both sufficient and necessary. | To explain the scenarios a reference diagram describing an example network will be used. It is as follows: [Q] [R] AS1 . . AS2 [A]----+----[SG-A].......+....+.......[SG-B]-------[B] ...... \ ..PI.. ----[btns-B] ...... [btns-C].....+....+.......[btns-D] Figure 1: Reference Network Diagram In this diagram, there are six end-nodes: A, B, C and D. Two of the systems are security gateways: SG-A, SG-B, protecting networks on which [A] and [B] reside. There is a node [Q] which is IPsec and BTNS capable, and node [R] is a simple node, with no IPsec or BTNS | capability. Nodes [C] and [D] are BTNS capable. | Nodes [C] and [Q] have fixed addresses. Node [D] has a non-fixed | address. | We will examine how these various nodes communicate with node SG-A, | and/or how SG-A rejects communications with some such nodes. In the | first example, we examine SG-A's point of view. In the second | example we look at Q's point of view. In the third example we look | at C's point of view. PI is the Public Internet ("The Wild"). |3.1. Example #1: A security gateway | The machine that we will care in this example is [SG-A], a firewall | device of some kind which we wish to configure to respond to BTNS | connections from [C]. | SG-A has the following PAD and SPD entries: Child SA Rule Remote ID IDs allowed SPD Search by ---- --------- ----------- ------------- |Williams & Richardson Expires January 27, 2008 [Page 6] |Internet-Draft BTNS IPsec July 2007 | 1 by-IP | 2 by-IP | 3 PUBLICKEY:any ANY by-IP | The last entry is the BTNS entry. Figure 2: SG-A PAD table | Note that [SG-A]'s PAD entry has one and only one wildcard PAD entry: | the BTNS catch-all PAD entry as the last entry, as described in | Section 2. and are from [RFC4301] section 4.4.3 Rule Local Remote Next Layer BTNS Action addr addr Protocol ok ---- ----- ------ ---------- ---- ----------------------- | 1 [A] [R] ANY N/A BYPASS | 2 [A] [Q] ANY no PROTECT(ESP,tunnel,AES, SHA256) | 3 [A] B-net ANY no PROTECT(ESP,tunnel,AES, SHA256) | 4 [A] ANY ANY yes PROTECT(ESP,transport, integr+conf) | Figure 3: [SG-A] SPD table | The processing by [SG-A] of SA establishment attempts by various | peers is as follows: | o [Q] does not match PAD entry #1, but does match PAD entry #2; PAD | processing stops, then the SPD is searched by [Q]'s ID to find | entry #2; CHILD SAs are then allowed that have [SG-A]'s and [Q]'s | addresses as the end-point addresses. | o [SG-B] matches PAD entry #1; PAD processing stops, then the SPD is | searched by [SG-B]'s ID to find SPD entry #3; CHILD SAs are then | allowed that have [SG-A]'s address and any addresses from B's | network as the end-point addresses. | o [R] does not initiate any IKE SAs; its traffic to [A] is bypassed | by SPD entry #1. | o [C] does not match PAD entries #1 or #2, but does match entry #3, | the BTNS wildcard PAD entry; the SPD is searched by [C]'s address and SPD entry #4 is matched. CHILD SAs are then allowed that have |Williams & Richardson Expires January 27, 2008 [Page 7] |Internet-Draft BTNS IPsec July 2007 | [SG-A]'s address and [C]'s address as the end-point addresses | provided that [C]'s address is neither [Q]'s nor any of [B]'s (see | Section 2). | o A rogue BTNS node attempting to assert [Q]'s or [B]'s addresses | will either match the PAD entries for [Q] or [B] and fail to | authenticate as [Q] or [B], in which case they are rejected, or | they will match PAD entry #3 but will not be allowed to create | CHILD SAs with [Q]'s or [B]'s addresses as traffic selectors. | o A rogue BTNS nodes attempting to assert [C]'s address will | succeed. Protection for [C] requires additional bindings of [C]'s | specific BTNS ID (that is, its public key) to its traffic flows | through connection-latching and channel binding, or leap-of-faith, | none of which are described here. |3.2. Example #2: A mixed end-system | [Q] is an NFSv4 server. | [Q] is a native IPsec implementation, and it's NFSv4 implementation | is IPsec-aware. | [Q] wants to protect all traffic with [A]. [Q] also wants to protect | NFSv4 traffice with all peers. It's PAD and SPD are configured as | follows: Child SA Rule Remote ID IDs allowed SPD Search by ---- --------- ----------- ------------- | 1 <[A]'s ID> <[A]'s address> by-IP 2 PUBLICKEY:any ANY by-IP The last entry is the BTNS entry. | Figure 4: [Q] PAD table Rule Local Remote Next Layer BTNS Action addr addr Protocol ok ---- ----- ------ ---------- ---- ----------------------- | 1 [Q] [A] ANY no PROTECT(ESP,tunnel,AES, SHA256) | 2 [Q] ANY ANY yes PROTECT(ESP,transport, | with integr+conf) | port 2049 |Williams & Richardson Expires January 27, 2008 [Page 8] |Internet-Draft BTNS IPsec July 2007 | Figure 5: [Q] SPD table | The same analysis shown above in Section 3.1 applies here with | respect to [SG-A], [C] and rogue peers. The second SPD entry permits | any BTNS capable node to negotiate a port-specific SA to port 2049, | the port on which NFSv4 runs. Additionally [SG-B] is treated as a | BTNS peer as it is not known to [Q], and therefore any host behind | [SG-B] can access the NFSv4 service on [Q]. As [Q] has no formal | relationship with [SG-B], rogues can impersonate [B] (i.e., assert | [B]'s addresses). |3.3. Example #3: A BTNS-only system | [C] supports only BTNS and wants to use BTNS to protect NFSv4 | traffic. It's PAD and SPD are configured as follows: Child SA Rule Remote ID IDs allowed SPD Search by ---- --------- ----------- ------------- 1 PUBLICKEY:any ANY by-IP | The last (and only) entry is the BTNS entry. Figure 6: Q PAD table Rule Local Remote Next Layer BTNS Action addr addr Protocol ok ---- ----- ------ ---------- ---- ----------------------- | 1 [C] ANY ANY yes PROTECT(ESP,transport, | with integr+conf) port 2049 | 2 [C] ANY ANY N/A BYPASS Figure 7: SG-A SPD table | The analysis from Section 3.1 applies as follows: | o Communication with [Q] on port 2049 matches SPD entry number 1. | This causes [C] to initiate an IKEv2 exchange with [Q]. The PAD | entry on [C] causes it to not care what identity [Q] asserts. | Further authentication (and channel binding) could occur within | the NFSv4 protocol. | o Communication with [A], [B] or any other internet machine |Williams & Richardson Expires January 27, 2008 [Page 9] |Internet-Draft BTNS IPsec July 2007 | (including [Q]), occurs in the clear, so long as it is not on port | 2049. | o All analysis about rogue BTNS nodes applies, but they can only | assert SAs for port 2049. |3.4. Miscellaneous comments | If [SG-A] were not BTNS-capable then it would not have PAD and SPD | entries #3 and #4, respectively in example #1. Then [C] would be | rejected as usual under the standard IPsec model [RFC4301]. | Similarly, if [Q] were not BTNS-capable then it would not have PAD | and SPD entries #2 in example #2. Then [C] would be rejected as | usual under the standard IPsec model [RFC4301]. |Williams & Richardson Expires January 27, 2008 [Page 10] |Internet-Draft BTNS IPsec July 2007 4. Security Considerations Unauthenticated security association negotiation is subject to MITM attacks and should be used with care. Where security infrastructures are lacking this may indeed be better than nothing. Use with applications that bind authentication at higher network layers to secure channels at lower layers may provide one secure way to use unauthenticated IPsec, but this is not specified herein. | The BTNS PAD entry must be last and its child SA ID constraints must | be non-overlapping with any other PAD entry, as described in section | 2, in order to ensure that no BTNS peer can impersonate another IPsec | non-BTNS peer. 4.1. Connection-Latching and Channel Binding BTNS is subject to MITM attacks. One way to protect against MITM attacks subsequent to initial communications is to use "connection | latching" [I-D.ietf-btns-connection-latching]. In connection | latching, ULPs cooperate with IPsec to bind discrete packet flows to | sequences of similar SAs. Connection latching requires native IPsec | implementations. MITMs can be detected by using application-layer authentication frameworks and/or mechanisms, such as the GSS-API [RFC2743], with | channel binding [I-D.williams-on-channel-binding]. IPsec "channels" | are nothing other than latched connnections. 4.2. Leap-of-Faith (LoF) for BTNS | "Leap of faith" is the term generally used when a user accepts the | assertion that a given key identifies a peer on the first | communication, despite a lack of strong evidence for that assertion, | and then remembers this association for future communications. | Specifically this is a common mode of operation for Secure Shell | [RFC4251] client. When a server is encountered for the first time | the Secure Shell client may ask the user whether to accept the | server's public key. If so, records the server's name (as given by | the user) and public key in a database. | Leap of faith can work in a similar way for BTNS nodes, but it is | currently still being designed and specified by the IETF BTNS WG. |Williams & Richardson Expires January 27, 2008 [Page 11] |Internet-Draft BTNS IPsec July 2007 |5. IANA Considerations | This document has no IANA considerations, neither seeking to create | new registrations nor new registries. (The new ID type is not used | on the wire, therefore it need not be assigned a number from the IANA | IKEv2 Identification Payload ID Types registry.) |Williams & Richardson Expires January 27, 2008 [Page 12] |Internet-Draft BTNS IPsec July 2007 |6. Acknowledgements | Thanks for the following reviewers: Stephen Kent |Williams & Richardson Expires January 27, 2008 [Page 13] |Internet-Draft BTNS IPsec July 2007 |7. References |7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. |7.2. Informative References [I-D.ietf-btns-connection-latching] Williams, N., "IPsec Channels: Connection Latching", draft-ietf-btns-connection-latching-00 (work in progress), February 2006. [I-D.ietf-btns-prob-and-applic] Touch, J., "Problem and Applicability Statement for Better Than Nothing Security (BTNS)", | draft-ietf-btns-prob-and-applic-03 (work in progress), | June 2006. [I-D.williams-on-channel-binding] Williams, N., "On the Use of Channel Bindings to Secure Channels", draft-williams-on-channel-binding-00 (work in progress), August 2006. | [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the | Internet Protocol", RFC 2401, November 1998. [RFC2408] Maughan, D., Schneider, M., and M. Schertler, "Internet Security Association and Key Management Protocol (ISAKMP)", RFC 2408, November 1998. [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [RFC2743] Linn, J., "Generic Security Service Application Program Interface Version 2, Update 1", RFC 2743, January 2000. [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol Architecture", RFC 4251, January 2006. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. |Williams & Richardson Expires January 27, 2008 [Page 14] |Internet-Draft BTNS IPsec July 2007 Authors' Addresses Nicolas Williams Sun Microsystems 5300 Riata Trace Ct Austin, TX 78727 US Email: Nicolas.Williams@sun.com Michael C. Richardson Sandelman Software Works 470 Dawson Avenue Ottawa, ON K1Z 5V7 CA Email: mcr@sandelman.ottawa.on.ca URI: http://www.sandelman.ottawa.on.ca/ |Williams & Richardson Expires January 27, 2008 [Page 15] |Internet-Draft BTNS IPsec July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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